A power IC (Integrated Circuit) device has been developed by integration of (i) a power MOS (Metal Oxide Semiconductor) transistor, which can deal with high voltage and/or high current and (ii) a control circuit for controlling the power MOS transistor. This is because the power IC device is used for an electric power management and an electric power controlling.
In particular, a DMOS (Double Diffused Metal Oxide Semiconductor) transistor has been attracting attentions as an efficient power MOS transistor. This is because the DMOS transistor can deal with high electric power required for an electric power supply and a motor control.
Regarding this power IC device, for example, patent document 1 discloses a power IC device in which a DMOS transistor and a CMOS transistor for controlling the DMOS transistor are integrated, as illustrated in FIG. 7.
As to the power IC device, it is efficient to use a trench power MOS transistor as a power MOS transistor such as a DMOS transistor. This allows an improvement in integration rate, i.e., this allows the surface of the silicon wafer to be further effectively utilized.
Note that the trench power MOS transistor means a power MOS transistor, which is formed by using a trench on the surface of a chip. In other words, a power MOS transistor, which is formed by using a trench dug on the surface of the tip.
This trench power MOS transistor can be applied to such a device structure disclosed in the patent document 1. Namely, a trench power MOS transistor and a control COMS transistor for controlling the trench power MOS transistor can be arranged so as to be integrated on the same chip.
Also, it is possible to improve the integration rate of the power IC device by using a trench power MOS transistor as a power MOS transistor. The reason is that a trench power MOS transistor requires smaller area on the surface of a silicon wafer than a DMOS transistor.
As another power IC device structure, unlike the structure that a power MOS transistor and a control CMOS transistor are integrated on the same chip, there is, for example, a structure that each transistor is formed on a separate chip, and is then built in the same package. This is for the purpose of reducing the manufacturing cost.    [Patent Document 1] Specification of U.S. Pat. No. 4,795,716 (issued on Jan. 3, 1989)